This invention relates generally to valve gated multi-cavity injection molding apparatus and more particularly to such apparatus including apparatus to simultaneously accurately drive all the valve pins between more than two positions.
Hydraulic mechanism for actuating injection molding valve pins is well known. However, in some applications such as those involving food, hydraulic fluid is not allowed in the mold. In these cases, pneumatic actuating mechanism is often used, but it does not have sufficient power for some requirements. The applicant's U.S. Pat. No. 4,212,627 which issued Jul. 15, 1980 shows mechanical mechanism for driving several valve pins simultaneously between the open and closed positions. While this two position actuating mechanism is satisfactory for many applications, it cannot be used for applications such as multi-layer molding where it is necessary to drive the valve pins between three or four positions during each injection cycle. Canadian Application Serial Number 2,192,611 to Schramm et al. which was laid open Aug. 20, 1997 also shows previous mechanism for simultaneously driving the valve pins.